how can I make the mobile navigation at the right side?

Hi there,

Can you give this CSS a shot?

.main-navigation.toggled .main-nav li a {
    display: flex;
    flex-direction: row-reverse;
    justify-content: space-between;
    padding-right: 20px !important;
}

Adding CSS: https://docs.generatepress.com/article/adding-css/

Let me know :)